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United States Patent |
5,647,731
|
Onozawa
|
July 15, 1997
|
Air compressor
Abstract
An air compressor in which oil loss due to the pressure in the cylinder
becoming negative during an unload can be prevented, thereby protecting an
outlet-side unloader valve. An air leak hole with a specific ventilating
resistance is formed between a valve body and a valve seat of an
intake-side unloader valve when the intake-side unloader valve is closed.
Also, a valve seat portion is provided, which cuts off a sliding portion
of the outlet-side unloader valve from the outlet passage when the
outlet-side unloader valve is opened.
Inventors:
|
Onozawa; Motoyuki (Higashimatsuyama, JP)
|
Assignee:
|
Zexel Corporation (Tokyo, JP)
|
Appl. No.:
|
431030 |
Filed:
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April 28, 1995 |
Foreign Application Priority Data
Current U.S. Class: |
417/295; 417/440; 417/557 |
Intern'l Class: |
F04B 049/02 |
Field of Search: |
417/295,364,440,557,297,298
|
References Cited
U.S. Patent Documents
3204857 | Sep., 1965 | Weller | 417/557.
|
3578883 | May., 1971 | Cheney | 417/295.
|
4229146 | Oct., 1980 | Errett | 417/281.
|
4370103 | Jan., 1983 | Tripp | 417/298.
|
4432698 | Feb., 1984 | Shirakuma et al. | 417/298.
|
4993922 | Feb., 1991 | Lauterbach et al. | 417/279.
|
5364240 | Nov., 1994 | Salecker | 417/427.
|
5503537 | Apr., 1996 | Schlossarczyk et al. | 417/296.
|
Foreign Patent Documents |
2-32875 | Sep., 1990 | JP.
| |
Primary Examiner: Thorpe; Timothy
Assistant Examiner: Korytnyk; Peter G.
Attorney, Agent or Firm: Wenderoth, Lind & Ponack
Claims
What is claimed is:
1. An air compressor comprising:
a cylinder;
a piston slidably mounted in said cylinder;
a cylinder head mounted on said cylinder, said cylinder head defining an
air inlet passage and an air outlet passage;
an inlet valve positioned between said cylinder and said air inlet passage
to permit air to flow from said air inlet passage into said cylinder in
response to movement of said piston in a first direction;
an outlet valve positioned between said cylinder and said air outlet
passage to permit air to flow from said cylinder into said outlet passage
in response to movement of said piston in a second direction;
an inlet-side unloader valve having a valve body and a valve seat, said
inlet-side unloader valve being mounted in said cylinder head and being
operable to close said air inlet passage;
an outlet-side unloader valve mounted in said cylinder head; and
an air leak hole having a specific ventilating resistance and being formed
in one of said valve body and said valve seat of said inlet-side unloader
valve.
2. The air compressor as claimed in claim 1, further comprising an air
conduit attached to said cylinder head for communicating with a governor
connected in parallel with an air tank, an air dryer, and a check valve.
3. The air compressor as claimed in claim 2, wherein said air conduit is in
communication with said inlet-side unloader valve and said outlet-side
unloader valve to permit communication with a discharge side of the
governor.
4. The air compressor as claimed in claim 2, wherein said inlet-side
unloader valve and said outlet-side unloader valve are capable of
operating in response to pressure from the governor when pressure in the
air tank exceeds a predetermined level.
5. The air compressor as claimed in claim 3, wherein said inlet-side
unloader valve and said outlet-side unloader valve are capable of
operating in response to pressure from the governor when pressure in the
air tank exceeds a predetermined level.
6. An air compressor comprising:
a hollow cylinder having a first end and a second end;
a piston slidably mounted in said cylinder to form a compression chamber;
a cylinder head mounted on a first end of said cylinder, said cylinder head
defining an air inlet passage and an air outlet passage;
an inlet valve positioned between said inlet passage and said compression
chamber to permit air to flow into said compression chamber;
an outlet valve positioned between said outlet passage and said compression
chamber to permit air to flow from said compression chamber;
an inlet-side unloader valve mounted in said cylinder head adjacent said
inlet passage, said inlet-side unloader valve including a holder, an
inlet-side unloader piston slidably fitted in said holder, and a valve
body slidably mounted in said holder and engaging said piston;
an outlet-side unloader valve mounted in said cylinder head adjacent said
outlet passage, said outlet-side unloader valve including an outlet-side
holder forming an interior space, an outlet-side piston slidably fitted in
said holder, and a valve body slidably connected to said holder for
blocking said outlet passage; and
a valve seat portion extending between one end of said outlet-side holder
and said discharge passage, said valve seat portion forming a recess for
receiving said valve body of said outlet-side unloader valve when said
outlet-side unloader valve is in an open position,
wherein said valve body of said outlet side unloader valve isolates said
interior space of said holder from said discharge passage when said valve
body of said outlet side unloader valve is received in said recess formed
by said valve seat portion.
7. The air compressor as claimed in claim 6, further comprising an air
conduit attached to said cylinder head for communicating with a governor
connected in parallel with an air tank, an air dryer, and a check valve.
8. The air compressor as claimed in claim 7, wherein said air conduit is in
communication with said inlet-side unloader valve and said outlet-side
unloader valve to permit communication with a discharge side of the
governor.
9. The air compressor as claimed in claim 8, wherein said inlet-side
unloader valve and said outlet-side unloader valve are capable of
operating in response to pressure from the governor when pressure in the
air tank exceeds a predetermined level.
10. The air compressor as claimed in claim 7, wherein said inlet-side
unloader valve and said outlet-side unloader valve are capable of
operating in response to pressure from the governor when pressure in the
air tank exceeds a predetermined level.
11. An air compressor comprising:
a cylinder;
a piston slidably positioned in said cylinder;
a cylinder head defining an air inlet passage and an air outlet passage;
an inlet valve located between said air inlet passage and said cylinder;
an outlet valve located between said cylinder and said air outlet passage;
an inlet-side unloader valve being mounted in said cylinder head, said
inlet-side unloader valve having a valve seat and a valve body for
blocking said air inlet passage in a closed position of said inlet-side
unloader valve;
an outlet-side unloader valve having a valve body for blocking said air
outlet passage;
an air leak hole having a specific ventilating resistance and being formed
in one of said valve body and said valve seat to permit limited air flow
to said cylinder when said inlet-side unloader valve blocks said inlet
passage; and
a seat portion forming a recess for housing said valve body of said
outlet-side unloader valve when said outlet-side unloader valve is in an
open position.
12. The air compressor as claimed in claim 11, further comprising an air
conduit attached to said cylinder head for communicating with a governor
connected in parallel with an air tank, an air dryer, and a check valve.
13. The air compressor as claimed in claim 12, wherein said air conduit is
in communication with said inlet-side unloader valve and said outlet-side
unloader valve to permit communication with a discharge side of the
governor.
14. The air compressor as claimed in claim 13, wherein said inlet-side
unloader valve and said outlet-side unloader valve are operable in
response to pressure from the governor when pressure in the air tank
exceeds a predetermined level.
15. The air compressor as claimed in claim 12, wherein said inlet-side
unloader valve and said outlet-side unloader valve are operable in
response to pressure from the governor when pressure in the air tank
exceeds a predetermined level.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an air compressor for use in an air piping
system through which compressed air is supplied to air brakes, air
suspension systems, automatic doors and the like.
2. Description of the Related Art
Generally speaking, an air piping system is constituted of an air
compressor 1 and an air tank 2 linked by piping via an air dryer 3 and a
check valve 4, as shown in FIG. 6. In the system, air is taken in and
compressed by the air compressor 1, temporarily stored in the air tank 2
after being dehumidified with a drying agent in the air dryer 3 and then
supplied to air brakes or the like via piping that is connected to the
outlet-side of the air tank. Also connected to the air tank 2 via the
piping is a governor 5, the exit side of which communicates with the
unloader valves on the intake side and the outlet side of the air
compressor 1 so that, when the pressure in the air tank 2 rises to a
specific level, the governor 5 enters the open state, to operate the
unloader valves, thereby setting the air compressor 1 in a decompression
state (unload state). Moreover, when the pressure in the air tank 2 drops
under a specific level, the governor 5 enters the closed state and is
reset to its initial state, to start the compression function of the air
compressor 1.
The air compressor disclosed in Japanese Unexamined Patent Publication No.
H2-32875 is an example of this type of air compressor. This air compressor
features a residual pressure forming valve which blocks off the
outlet-side passage when the unload valve provided in the intake-side
passage is closed, in order to suppress, as much as possible, any negative
pressure in the cylinder during an unload and to prevent oil from being
drawn up into the cylinder. According to this invention, with the residual
pressure forming valve blocking off the outlet passage, discharge of the
air inside the cylinder during an up-stroke of the piston is inhibited, to
maintain the pressure in the cylinder at a high level, and since, even
when the piston enters the down-stoke, the pressure in the cylinder does
not become extremely negative, preventing the pressure in the cylinder
from becoming negative.
However, in the example quoted above, since there is no air supply to the
cylinder during an unload, if the unload time is long, the air in the
cylinder overflows into the crank chamber through the gap between the
cylinder and the piston, reducing the pressure in the cylinder, which may
then become negative.
Furthermore, since the air that is thus released contains oil, carbon and
the like in the cylinder, there is a likelihood of these substances, i.e.,
oil, carbon and the like, adhering to the sliding area of the residual
pressure forming valve (outlet-side unloader valve), which may cause
operational failure. Also, there is a likelihood of the valve body making
a fluttering movement due to the pressure wave of the outlet pressure of
the outlet air and becoming worn.
SUMMARY OF THE INVENTION
The object of the present invention is to provide an air compressor in
which pressure in the cylinder does not become negative during an unload,
so that loss of oil can be prevented and, at the same time, the
outlet-side unloader valve can be protected.
Accordingly, in order to prevent the pressure in the cylinder from becoming
negative during an unload, the first mode of the present invention is an
air compressor having an intake passage for taking air into the cylinder
via an intake valve through reciprocal movement of a piston, an outlet
passage for discharging compressed air to the air tank side via an outlet
valve, an intake-side unloader valve for blocking off the intake passage
when the pressure in the air tank exceeds a specific level and an
outlet-side unloader valve for blocking off the outlet passage. The air
compressor is further provided with an air leak hole having a specific
level of ventilating resistance. The air leak hole is formed between the
valve body and the valve seat of the intake-side unloader valve when the
intake-side unloader valve is closed.
Thus, due to the air leak hole, which has a specific level of ventilating
resistance between the valve body and the valve seat of the intake-side
unloader valve when the intake-side unloader valve is closed, a specific
quantity of air is taken in through the air leak hole during the piston
down-stroke and compressed during the piston up-stroke, to maintain the
pressure in the cylinder at a specific level, thereby preventing it from
becoming negative. Note that since the air that blows by through the gap
between the cylinder and the piston is constantly replenished with air
taken in through the air leak hole, the pressure in the cylinder is
maintained at a specific level even when the unload time is long.
In addition, in a second mode of the present invention, in order to protect
the outlet-side unloader valve, is an air compressor including an intake
passage for taking air into the cylinder via an intake valve through the
reciprocal movement of a piston, an outlet passage for discharging
compressed air to the air tank side via an outlet valve, an intake-side
unloader valve for blocking off the intake passage when the air in the air
tank exceeds a specific level and an outlet-side unloader valve for
blocking off the outlet-side passage. It is further provided with a seat
portion for accommodating the valve body of the outlet-side unloader valve
to cut off the sliding portion of the outlet-side unloader valve from the
outlet passage when the outlet-side unloader valve is open.
Thus, due to the seat portion for blocking off the sliding portion of the
unloader valve from the outlet passage when the outlet-side unloader valve
is open, the outlet air is prevented from entering the sliding portion of
the unloader valve and, at the same time, since the valve body is housed
and held in the seat portion, the valve body does not vibrate and become
worn due to the pressure wave of the outlet air.
Furthermore, according to a third mode of the present invention, in order
to achieve the goals described earlier all at once, is an air compressor
including an intake passage for taking air into the cylinder via an intake
valve through the reciprocal movement of a piston, an outlet passage for
discharging compressed air to the air tank side via an outlet valve, an
intake-side unloader valve for blocking off the intake passage when the
pressure in the air tank exceeds a specific level and an out-let-side
unloader valve for blocking off the outlet passage. It is further provided
with an air leak hole formed between the valve body and the valve seat of
the intake-side unloader valve when the intake-side unloader valve is
closed that has a specific level of ventilating resistance, and a seat
portion for accommodating the valve body of the outlet-side unloader
valve, to cut off the sliding portion of the unloader valve from the
outlet passage when the outlet-side unloader valve is open.
Consequently, since it is provided with the features of the first and
second modes of the present invention, the goals described earlier can be
achieved all at once.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other features of the invention and the concomitant
advantages will be better understood and appreciated by persons skilled in
the field to which the invention pertains in view of the following
description given in conjunction with the accompanying drawings which
illustrate a preferred embodiment. In the drawings:
FIG. 1 is a cross section showing the structure of the air compressor
according to an embodiment of the present invention;
FIG. 2 is a cross section illustrating the process of the piston
down-stroke during a load of the air compressor shown in FIG. 1;
FIG. 3 is a cross section illustrating the process of the piston up-stroke
during a load of the air compressor shown in FIG. 1;
FIG. 4 is a cross section illustrating the process of the piston up-stroke
during an unload of the air compressor shown in FIG. 1;
FIG. 5 is a cross section illustrating the process of the piston
down-stroke during an unload of the air compressor shown in FIG. 1; and
FIG. 6 is a block diagram of an air piping system in which the air
compressor is used.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The following is an explanation of an embodiment of the present invention
with reference to the drawings.
An air compressor 1 shown in FIGS. 1-5 is directly linked with an engine
(not shown) via a timing gear and it is constantly rotated as long as the
engine is driven. A piston 7 reciprocates in the cylinder 8 via a
connecting rod 6 which is provided inside a crank chamber 70 to change the
volumetric capacity of a compression space 60.
In the upper portion of the cylinder 8, an intermediate member 10 is
provided, in which a cooling water passage 9 is formed. A cylinder head 11
is secured above the intermediate member 10. In the intermediate member
10, through holes 12a and 12b are formed. At an open end of the through
hole 12a on the cylinder side, an intake valve 17 is provided and at the
open end of the through hole 12b on the cylinder head side an outlet valve
18 is provided. In addition, the cylinder head 11 is provided with a
communicating hole 13a which extends from one side surface of the cylinder
head to a. Also, communicating hole 13b extends from the other side
surface of the cylinder head to the bottom surface. The communicating hole
13a is connected with the through hole 12a to constitute an intake passage
14 and the communicating hole 13b is connected with the through hole 12b
to constitute an outlet passage 15. An intake-side unloader valve 19 is
provided in the intake passage 14 for opening and closing the intake
passage 14 and an outlet-side unloader valve 20 is provided in the outlet
passage 15 for opening and closing the outlet passage 15.
The intake-side unloader valve 19 includes an unload piston 22, fitted
inside a holder 21, which is mounted in the upper portion of the cylinder
head 11 in such a manner that it can slide freely. A valve body 23 is
provided and is in contact with the unload piston 22 and a valve seat 24
is provided on the intake passage 14 as a part of the cylinder head 11
which faces opposite the valve body 23. In addition, the valve body 23 is
provided with an air leak hole 40 formed as a notch of a specific size so
that when the valve body 23 is seated in the valve seat 24, the intake
passage 14 is opened with a specific level of ventilating resistance.
Moreover, the air tightness between the unload piston 22 and the holder 21
is maintained with an O-ring 25 provided around the unload piston 22, and
a spring 27 is provided between a spring receptacle 23a formed at the base
portion of the valve body 23 and a spring receptacle 26 provided under the
holder 21. This spring 27 applies a constant force to the unload piston 2
in the direction which moves it away from the valve seat 24. The piping 28
which communicates with the governor 5 shown in FIG. 6 is connected to the
upper end of the holder 21 and compressed air from the air tank 2 is
supplied to the upper end of the unload piston 22 through a hole 29 formed
in the piping 28 so that the unload piston 22 can be pressed down against
the resistance or bias of the spring 27.
In the outlet-side unloader valve 20, an unload piston 31 is fitted inside
a holder 30 which is mounted in the cylinder head 11 in such a manner that
it slides freely. A valve body 32, which is in contact with the unload
piston 31, is seated in a valve seat 33, provided on the outlet passage 15
as part of the cylinder head 11 facing opposite the valve body 32, to
block off the outlet passage 15.
The air tightness between this unload piston 31 and the holder 30 is also
maintained with an 0-ring 34 which is provided at the holder 30. A spring
35 is provided between a spring receptacle 32a, formed in the base portion
of the valve body 32, and a spring receptacle 30a provided under the
holder 30. This spring 35 applies a constant force to the unload piston 31
in a direction which moves it away from the valve seat 33. The piping 28
which communicates with the governor 5 shown in FIG. 6 is connected to the
upper end of the holder 30 and compressed air from the air tank 2 is
supplied to the upper end of the unload piston 31 through a hole 36 formed
in the piping 28, so that the unload piston 31 can be pressed down against
the resistance or bias of the spring 35.
The valve body 32 is housed in a seat portion 50 which is formed as part of
the cylinder head 11 extending toward the inside while maintaining a
specific diameter in the vicinity of the lower end of the holder 30 at a
position at which the unload piston 31 is biased upwardly by the spring
35, i.e., at the so-called load position and since the valve body 32 is
seated in the lower end portion of the holder 30, it shuts off the sliding
portion of the outlet-side unloader valve 20, which includes parts such as
the unload piston 31 and the like, from the outlet passage 15.
In the air compressor 1 structured as described above, when the air
pressure in the air tank 2 is below a specific level, as shown in FIGS. 2
and 3, the governor 5 is in a closed state. This means that compressed air
is not supplied to the intake-side unloader valve 19 or to the outlet-side
unloader valve 20 and that the air compression function of the compressor
is in progress with the reciprocal motion of the piston 7 while the intake
passage 14 and the outlet passage 15 are in an open state (load).
In other words, during the down-stroke process of the piston 7, as shown in
FIG. 2 (the intake process), the volumetric capacity of the compression
space 60 increases and the pressure in the compression space becomes
negative. As a result, when the outlet valve 18 closes, the intake valve
16 opens so that air flows into the compression space 60 via the intake
passage 14. Then, during the up-stroke process of the piston 7 shown in
FIG. 3 (the compression / discharge process), the volumetric capacity of
the compression space 60 becomes reduced to increase the pressure inside.
The intake valve 17 is closed and, at the same time, the outlet valve 18
is opened, to supply air to the air dryer 3 via the outlet passage 15. At
this point, the valve body 32 of the outlet-side unloader valve 20 is
housed in the seat portion 50 formed in the cylinder head 11 and is seated
on the lower side surface of the holder 30 to cut off the unload piston 31
side from the outlet passage 15.
With this, substances such as oil and carbon contained in the air which is
discharged are prevented from entering the area where the unload piston 31
is in contact with the holder 30, thus preventing operational failure in
the sliding area. Moreover, the valve body is prevented from making a
fluttering movement due to a pressure wave or flow of the outlet air which
occurs when air is let out through the outlet valve causing the valve to
become worn.
In contrast, when the air pressure in the air tank 2 exceeds a specific
level, as shown in FIGS. 4 and 5, the governor 5 enters an open state and
compressed air is sent from the piping 28 through the holes 29 and 36 to
the intake-side unloader valve 19 and the outlet-side unloader valve 20 so
that the unload pistons 22 and 31 are pressed down against the resistance
of the springs 27 and 35 respectively, to seat the valve bodies 23 and 32
in the valve seats 24 and 33 respectively (unload). In this condition, the
outlet passage 15 is completely blocked off and the intake passage 14 is
in communication only through the air leak hole 40.
When the piston 7 is in the up-stroke process (compression process) during
an unload operation, as shown in FIG. 4, the residual air in the
compression space 60 is compressed and would be discharged through the
outlet valve 18. However, since the outlet passage 15 is blocked off by
the outlet-side unloader valve 20, this air is not let out, instead, it is
compressed within the compression space 60. During this compression
process, since the pressure in the compression space 60 becomes high, a
small quantity of the air in the compression space 60 leaks out as blow-by
through the gap between the piston 7 and the cylinder 8 toward the crank
chamber 70. Consequently, the compressed air pressure of the residual air
becomes gradually lowered to a specific level. Note that in order to
prevent the pressure in the compression space 60 from being applied to the
intake valve 17 in its entirety, the intake-side unloader valve 9 blocks
off the intake passage 14.
Also, during the down-stroke process of the piston 7 (leak-air intake
process), as shown in FIG. 5, if the pressure in the compression space 60
drops under a specific level due to the blow-by during the compression
process described above, a specific quantity of air is taken in to the
compression space 60 through the air leak hole 40 for replenishment. Thus,
the quantity of air being compressed in the compression space 60 is
maintained constant at all times. Because of this, even when the unload
time is long, the pressure in the compression space 60 is prevented from
becoming negative due to the blow by and oil loss can be prevented on the
crank chamber 70 side.
Note that if the intake-side unloader valve 19 is not provided with an air
leak hole, then when it is opened during the leak-air intake process
described earlier, a specific quantity of air is taken in from the intake
passage 14 to be compressed, as in the case of a load operation. This will
result in the air pressure in the compression space 60 exceeding a
specific level. Consequently, the valve body 32 of the outlet-side
unloader valve 20 is pressed upward to discharge air. In order to prevent
this, if the closing force of the unloader valve 20 is increased, the
pressure in the compression space will also increase, reaching
approximately 30-40 Kgwt/cm.sup.2 with the piston at the top dead center.
This increases the drive peak torque, which results in an increase in the
power loss at the air compressor. The air leak hole 40 is formed with a
specific diameter (specific passage resistance) in the unloader valve 19
to solve this problem. Note that while in this embodiment the air leak
hole 40 is formed in the valve body 23 of the unloader valve 19, similar
advantages can be achieved with an air leak hole formed on the valve seat
24 side.
As has been explained, according to the present invention, since an air
leak hole with a specific level of ventilating resistance is formed
between the valve body of the intake-side unloader valve and the valve
seat when the intake-side unloader valve is closed, the quantity of air
that blows by during the compression process in an unload operation can be
replenished by taking air into the compression space through the air leak
hole, thus preventing oil loss into the compression space.
Furthermore, since the seat portion is provided for housing the valve body
of the outlet-side unloader valve to cut off the sliding portion of the
outlet-side unloader valve from the outlet passage when the outlet-side
unloader valve is open, oil, carbon and the like are prevented from
adhering to the sliding portion of the outlet-side unloader valve during a
load. Thus, operational failure in the sliding portion is prevented. At
the same time, the valve body is prevented from becoming worn due to a
fluttering movement caused by a pressure wave or flow of the outlet air,
thereby achieving stabilization of operation of the outlet-side unloader
valve and also increasing its service life.
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